CYCLIC VARIATION OF THE POWER OF ULTRASONIC DOPPLER SIGNALS BACKSCATTERED BY POLYSTYRENE MICROSPHERES AND PORCINE ERYTHROCYTE SUSPENSIONS

Factors affecting the power of the ultrasonic Doppler signal within th e flow cycle have been evaluated experimentally using a pulsatile flow loop model. Polystyrene microspheres and porcine red cells suspended in saline solution for hematocrits between 2 and 40% were used as scat tering fluid in the flow model. Experiments were performed at mean flo w velocities of 11, 64, and 76 cm/s. In laminar flow experiments perfo rmed at a mean velocity of 11 cm/s, no variation of the Doppler power was found for both polystyrene microspheres and red cell suspensions ( 40% hematocrit). When turbulence was induced in the flow model, the po wer increased during systole, a maximum was observed early after peak systole, and a decrease was obtained in diastole during deceleration o f flow. At higher mean flow velocities (64 and 76 cm/s), a significant cyclic variation of the Doppler power was also measured for all value s of hematocrits (between 2 and 40%). The power of the signal scattere d by microspheres and red cell suspensions at 4% hematocrit dropped in systole, reached a minimum at peak systole, and then increased during early diastole. For red cells suspended in saline at 40% hematocrit, a slightly different pattern of variation was obtained. The cyclic var iations observed at high flow velocities and in the presence of turbul ence are believed to be associated with cyclic changes in the correlat ion among particles. In the present study, the effect of red cell aggr egation on the cyclic variation has not been addressed.